Liquid phase - boo



Aug. 11, 1'959 R. W. KREBS ET AL COKING HEAVY OILS WITH INERT SOLIDS `INTWO STAGES Filed Oct. 30, 1953 ALTE R NAT IVE PRODUCT COKE LIFT GAS

4- SHOT SLURRY Ji N STRIP GAS INVENTORS ROBERT W. KREBS CHRLESN.KIMBERLIN,JR

ATTORNEY United States Patent O COKING HEAVY OILS WITH INERT SOLIDS INTWO STAGES Robert W. Krebs and Charles N. Kimherlin, Jr., Baton Rouge,La., assignors to Esso Research and Engineering Company, a `corporationof Delaware Application October '30, 1953, Serial No. 389,360 6 Claims.(Cl. 208-53) The present invention relates to improvements in cokingheavy oils. The invention relates more specifically to a process and anapparatus for'converting petroleum residua and other heavy hydrocarbonoils by treating them rst in liquid phase and under mild conditions andsubsequently treating the unconverted oil more drastically in vaporphase by contacting with mobile, hot solid particles of catalyticallyinert material. Preferably, in the first coking stage relatively `coarseparticulate heatecarrying solids are passed downwardly by gravitythrough the oil primarily in liquid'phase, to cause partial conversionto vapor products, and the feed is then contacted at higher temperaturesand primarily in vapor phase With other and more finely dividedheatcarrying solid particles. In the preferred embodiment of theinvention, the latter particles are in the form of a uid bed. In somecases and for some purposes, however, they may be contacted in atransfer line or even in a non-fluid but moving bed.

In the conversion of heavy hydrocarbon oils by coking, it has been knownfor some time that product distribution is more satisfactory if thecoking is carried out` at fairly low temperature. Higher temperaturesresult in increasing proportions of gaseous and coke products withcorresponding reduction in proportions of products which boil within themotor fuel and gas oil ranges. In coking to produce motor fuels, it isparticularly desirable to produce a large proportion of good quality gasoil which can be converted in turn, by a conventional catalytic crackingoperation, into a high grade motor fuel.

Despite the advantages of iluid bed coking, this type of conversionprocess has centain definite limitations at lower temperature ranges.Feed rates must be lowered considerably at temperatures below aboutl000'F. to avoid bogging the fluid bed. For this reason there arecertain advantages in the older and more conventional delayed cokingoperation when it is desired tov operate at relatively low temperatures.However, the conventional delayed coking process, which uses a soakingdrum that must be cleaned out periodically, is quite objectionable inother respects. In the prior art, delayed coking operations commonly areat about 900 F.

Hence, an object of the present invention is to obtain asvfar aspracticable the advantages of both systems in a single system, withoutsome of their disadvantages.

According to the present invention, the objectionable deposition of-coke in a delayed coking drum is largely and in many cases completelyavoided by passing heatcarrying solids of coarse particle side, forexample shot or shot-like particles, through the drum to serve as basesfor the deposition of coke and to keep the drum walls relatively clean.In this way the coke formed during mild conversion of the feed iscarried out of the drum so that it can remain in service continuously.This removes a major limitation on this type of operation.

'Conversion at mild conditions gives good product disicc drastic enoughto obtain high conversion levels. To

raise the conversion levels, according to the present invention, theunconverted feed in the rst stage is used to slurry the coarseheat-carrying particles or vshot and the slurry of oil and solidparticles is then taken to a second and more drastic conversion stage.In this stage other heat-carrying particles, preferably more finelydivided on the average than the first, carry on the conversion.Preferably the latter solids are in the form of a turbulent, uidized bedand in such quantity and` at such a temperature level that thisconversion stage is largely -in vapor phase. Upon contacting the hotparticles in the second stage, the unconverted feed from the first stageis rapidy vaporized and cracked thermally. The coarse solids orshot-like particles which were carried into lthe second stage in aslurry are rapidly dried, the oil deposited thereon being vaporized andcoked. The proportions of hot solids to liquid feed in this second stageare such that the uid bed at all times is substantially dry and freefrom agglomeration and bogging. While operating conditions may vary fordifferent feed stocks and for different types and proportions of hotparticulate solids, it is preferred to operate the first stage at atemperature range between about 800 and 900 F. and for a time sufficientto accomplish substantial but not complete conversion of the feed.Residence or coking time in this first or liquid stage may vary fromabout l0 minutes to 4 hours or more. The second stage coking in thefluid bed is carried out at a substantially higher temperature,preferably appreciably above 900 F., a desirable range being betweenabout 950 and 1050 F. This raises the over-all conversion to a highlevel without excessive conversion to coke and/or gas and the combinedproduct is satisfactory in quantity and quality. Y

After the coarse solids have passed into the fluid bed, carrying cokedeposited thereon in the first or liquid conversion phase, they arerapidly dried. Along withj the solids which comprise the fluid bedproper, they growl in particle size by accretion of coke layersdeposited thereon. The temperature of the bed must be maintained in theface of the endothermic reaction and the feed vapozation heatrequirements. Hence, the solids, both coarse and fine, are circulated toa heater or burner where they are reheated and then recycled. ReheatingYis preferably accomplished by burning part of the prod-I finely dividedsolids which comprise the fluid bed or the bulk thereof also arepreferably coke particles of particle size between about 20 and 400microns in average diameter. Some of the latter may overlap in size n.rangel the larger or shot-like particles. If materials other: p

tribution in some respects, as noted above, butit is not 'than coke areused for the coarse particles, excessive coke burning may be required inthe heatento decoke them. Y y,

The system preferably is so operated that about 70 to.V

%, preferably about 85%, of the total conversion takes".

yplace in the soaking zone (liquid phase at low'tempeaf-l' ture).Formation of coke precursors, soft spongy solids, in this zone mayamount to 10-l5% or more, based on Weight ofthe feed. Hence, most of theliquid products are producedin the mild rst stage, but most oftlfecok'e' production (which may total 10 to 25% of the totalfed or more-with some feed stocks) is produced in the second or iluid bed zonewhere the operating temperature is considerably higher. In conventionaldelayed coking, and in the first phase of the present process, as muchas l to 20% or more of soft solid coke may be produced. In -the presentcase, however, this soft coke-like material is substantially convertedin the second phase lso that rthe over-all production of coke of lowvolatile content may be less than the apparent coke formed in the firststage. Over-all conversion to liquid products is higher and qualitybetter than in single phase uid coking at the same temperature and feedrate.

The invention will be more fully understood with reference to thedetailed description of a presently preferred embodiment thereof whichis illustrated diagrammatically in the accompanying drawing.

Referring to the drawing, a colting drum or vessel 11 is adapted toreceive a liquid residuum or other heavy oil feed stock through a feedline 13. The feed may be preheated in a coil or heater, not shown, to atemperature up to 800 F. or so. The preheat temperature should not besufficiently high to cause coke deposition in the coil or otherpreheater but is preferably about as high as can be tolerated withoutsuch deposition. The feed is converted primarily in liquid phase in thevessel 11 which is somewhat analogous to the conventional delayed cokingdrum.

In the conventional coking drum, however, although the oil is usuallyagitated, coke is formed in substantial quantities on the walls of thedrum which finally becomes so completely lled that it must be taken outof service and the coke removed. In the present invention, the drumremains in service continuously, at least for a long period of time. Astream of coarse solids or shot, that is, solid heat-carrying particlesof somewhat larger size than conventional fluidized solids, is suppliedthrough a line 15 having a manifold outlet 17 in the top of the drum 11.The shot, preferably particles of coke of 100 to about 500 micronsaverage diameter, ows out of the manifold outlet nozzle 17 and drops bygravity through the liquid oil in the vessel 11. These particles arepreheated to such a temperature as to maintain within the drum a cokingtemperature between 800 and 900 F. The feed rates of the oil and theshot or other coarse particles are adjusted so as to keep the oil in thevessel for a sufficient time to convert a major portion thereof by mildcracking into vapor or vaporizable products such as gasoline and gasoil. These products pass overhead through a line 19. At a cokingtemperature in the liquid phase, for example, of 900 F., someconstituents boiling at more than 900 F. may be carried over with thevapors overhead and at the same time some components boiling below 900F. may remain in @the liquid. In other words, this system does not andneed not give clean cut separation at a sharply defined cut point. In anaverage case, perhaps 40 to 50% of the feed will go overhead in the rststage, the remainder passing in the slurry to the second stage.

Some coke is deposited on the particles falling through the oil invessel 11 but coke which tends to deposit on the walls of the vessel isconsistently scrubbed olf by the falling particles. Thus cokeaccumulates on the coarse particles and is flushed with the particlesfrom the bottom of vessel 11 through an outlet 21. This product,consisting of an oil slurry carrying the shot and the coke depositedthereon, is conveyed by a pump 23 through a line 25 to a fluid solidsbed in a vessel 27.

T he shot and coke slurry taken from the primary coke drum 11 isdistributed through a plurality of nozzles 29 into a uid bed ofpreheated solid particles operating at a temperature preferably between950 and 1050 F.

This fluid bed preferably comprises a high proportion of coke particlesof substantially smaller size than the shot which are rained through theliquid phase in drum 11. A desirable particle size for the fluid bedcoke is between 20 and 200 microns although some particles may be aslarge as 400 microns average diameter. Upon contact with the hot solidsin the bed of the second stage, the more volatile constituents of theslurry are quickly vaporized, whereas the less volatile begin to crack.

As indicated, the above operation of a uid bed at a temperature above950 F. is more satisfactory and efcient from the standpoint of capacitythan operation at a lower temperature. Data have been obtained inlaboratory tests indicating that for each 30 to 50 F. below 950 F. thefeed rate to a fluid bed must be cut in half. Conversely for each 30-50"F. above 950 F. the feed rate may be doubled. Hence, the capacity of auid bed coking unit is extremely dependent upon the operatingtemperature. For this reason a substantial part of the coldng is carriedout, where the character of the feed stock permits, in the coking drumpreferably leaving Y mainly a very heavy residuum for conversion in thefluid bed. As indicated above, however, some lower boiling constituentsare carried over since a sharp cut is not obtained in the liquid stageoperation. The fluid solids bed is operated at a higher temperature thanwould be desirable for good product distribution if the whole feed werecracked in the fluid bed. This results in good product distribution fromthe rst stage plus a high conversion level in the second ait higher feedrates than otherwise would be possible.

In order to carry out the uid bed coking operation, a stream of hotcoke, of particle size smaller, on the average, than the coarseparticles in the first stage, is supplied to an upper portion of a bedthrough a line 31 leading from a burner or heating vessel 33.Vaporization and cracking are rapid and the coker products, in vapor orgaseous form, pass overhead through a solids separator such as a cyclone35. The separated solids are returned to a fluid bed through a solidline 37. The vapor products from the second stage, now free from solids,pass overhead through a line 39 to join the products from the pri marycoking phase in line 19. Both products are taken to a suitablefractionation and recovery system of a conventional type, not shown. Ifdesired, the products may be recovered separately to avoid mixing theproducts from line 39 with those from line 19. The latter tend to becomemore unsaturated with increased coking temperatures.

The slurry feed rate through line 25 to the fluid bed should be adjustedso that the uid bed remains substantially dry, in order that nosubstantial agglomeration and bogging of the bed can take place. Thespent solids, both tine and coarse, are withdrawn from the bottom of thecoker vessely 27 through a stripping section 41, a steam line 43 beingprovided for stripping the occluded conversion products from the coke.The coke is then returned through a return bend 45 and line 47 to theburner or heater 33. Product coke may be withdrawn from the systemthrough line 49 or from the burner side if desired. It will beunderstood that both the large particles or shot, which were passedthrough the first or liquid stage, and the -fluidizable coke, whichforms the bulk of the fluid bed in vessel 27 and which did not gothrough .the first stage, pass through line 45, 47 to the burner orheater.

The burning vessel or heater 33 is adapted to contain a fluidized bed ofcoke, all the heat carrying solids, e.g. coke, including the nelydivided solids which supply the heat to iluid bed 27 and the coarsesolids which supply the heat to the liquid phase coker. These solids areall reheated by burning part of .the coke therefrom in the preferredarrangement. However, where product coke is of sufficient value,extraneous fuel such as gas, torch oil, or the like may be introducedwith the air or oxygen which supports combustion within the burner.

The burner vessel contains a baille 51 which connects with a standpipefor reheated solids to be returned to the fluid coking bed. It isconnected to line 53 and return bend S which in turn is connected to theud bed feedline 31 previously described.l Appropriate valves may beprovided in both of the lines 31 and 47, etc., to control' Part of thesolids in burner vessel 33 flow downwardly? from the bottom of thevessel through a line 61 into an elutriator 63. The latter may be of anysuitable type such as a packed or partially packed column within whichan upow stream of air or oxygen, introduced through line 65, is flowing.

The arrangement is such that the relatively ne vsolids are carriedupwardly by elutriation through a line 67 and returned to the burner,whereas the coarse solids ow downwardly by gravity through line 69 andare returned through line 1-5 to the liquid phase coking drum 11. Alifting gas, such as steam or hydrocarbon gas, is introduced at 71 topropel the coarse solids or sho back to the coking drum.

Instead of withdrawing product coke through line 49, it may be withdrawnthrough a branch line 73 from line 67 as indicated in the drawing. Thisarrangement ayoids the withdrawal of the coarse coke particles which maybe needed inthe liquid phase coker.

It will be observed that suitable aeration gases may be introduced intothe various lines as required and that the apparatus may be modified invarious ways as will be apparent to those skilled in the art. The fluegases from the burner pass upwardly through a separator 75 and an outlet77, entrained solids being returned to the burner bed through line 79 inconventional fashion.

In general, operation in the first stage at a temperature as low as 800F. will require a residence time of up to 4 hours or so. At 900 F. aresidence time in the neighborhood of 30 minutes in the liquid phase maybe found ample. It will be understood that the passage of the hot coarseparticles or shot through this stage accomplishes several results notfound in conventional delayed coking operations. These include (l) thesupply of most of the heat by the hot solids, eliminating drasticpreheating and resultant coke deposition in heating coils, etc., (2) thecoarse particles provide a very large total surface for coke deposition,the wall surface of the drum being comparatively very minor, (3) thefalling shot tend to abrade off the walls any incipient coke formationstending to deposit thereon. All three of these effects help to keep theapparatus clean. `It is not necessary to dangle chains and otherapparatus down into ythe coking drums, to be pulled out by a heavytractor or locomotive when the drum cokes full, as has frequently beendone in the prior art. Another advantage is that the fluid bed of Ithesecond phase is not only a coking zone but also a vaporization zone fora part of the feed. As noted above, a sharp cut point is not obtained inthe first stage, moreover the downflowing coarse hot particles continueto visbreak the feed in the drum as it flows down and out through theslurry line. Appreciable proportions of relatively lowboiling fractionsare promptly ashed olf upon entry into the hot iluid solids bed of thesecond stage.

The present application is a continuation in part of application SerialNo. 232,523, allowed U,S. 2,775,546, of the present inventors, filedJune 20, 1951. In the parent application a solids bed is used to flashlow boiling conversion products and some solids are recirculated to aliquid phase coking stage.

While the above description has referred to the use of coke as theheat-carrying solid material, sand ceramic beads, mullite shot, metallings, shot, and other materials may be substituted. Coke is preferredin most cases because of its ready availability as a product of theprocess. By using coke it is not necessary to continue burning in theheater vessel 33 until all of the coke deposited is removed from thecoarse particles to be returned verted to coke and vapors; theimprovement whichcomtothe liquid phase coker. This frequently is ofconsider-` able advantage.

K What is claimed is:

l. In a combination hydrocarbon oil fluid coking process wherein an oilis initially subjected to relatively mild long time conversionconditions at a temperature in the range of 800 to 900 F. in a liquidphase delayed coking zone to cause substantial conversion to vapors andc vaporizable liquid, and then the unconverted liquid resi- 1'0 due ofsaid oil and said vaporizable liquid are passed to the fluid coking zoneof a two-vessel hydrocarbon oil fluidized solids coking systemcomprising a fluid coking zone and a heating zone to be furthercompletely conprises'passing preheated shot of relatively large particlesize downwardly through said liquid phase delayed coking zone to supplya major lportion of the necessary heatv thereto and to remove cokeprecursors therefrom, passing said shot along with the vaporizableliquid and unconverted liquid residue to said fluid coking zone wherebysaid shot is dried, then owing said shot to said heating zone along withthe portion of the fluidized solids transferred from said iluid cokingzone to said heating zone to be reheated therein, and separating andreturning said shot so reheated to said delayed coking zone.

2. The process of converting heavy oil to more volatile products whichcomprises contacting oil feed in liquid phase with a mass of preheatedparticles of solid heat transferring material of suicient particle sizeto fall freely by gravity through said oil and in suicient mass tomaintain a liquid phase coking temperature between about 800 and 900 F.for a sufficient contact time to accomplish substantial conversion tovapors and vaporizable liquid products, removing vapor productstherefrom, flowing a stream of said particles in a slurry of the liquidproducts and unconverted oil to a fluid bed coking zone containing amass of finer particles, contacting said liquid products and unconvertedoil in said zone with a sufficient mass of preheated iluidized solidheat carrying particles to vaporize and crack the liquid products andunconverted oil under substantially dry fluid bed conditions,withdrawing vaporous products, withdrawing solids from said fluid bedzone to a heating zone, separating finer particles from the coarseparticles, and passing heated coarse particles to the top of the liquidphase, said coarse particles passing downwardly therethrough by gravity.

3. The process of claim 2 wherein the coarse particles are cokeparticles of at least 100v microns average diameter.

4. The process of converting heavy oil feed to more vvolatile productswhich comprises maintaining said oil in a liquid mass in a delayedcoking zone at a temperature of G-900 F., downwardly passing by gravityheated, relatively coarse solids having an average diameter of at leastmicrons through said liquid mass to supply at least a major part of theheat necessary to preserve said temperature thus causing substantialconversion of said oil in the liquid phase to vapors and coke, said cokedepositing on said coarse particles, passing a slurry of unvaporized oiland said coarse particles to a fluid bed coking zone, said iluid bedcoking zone containing a mass of relatively iiner particles at atemperature above 900 F., contacting said slurry with said bed of finerparticles to vaporize and crack said unvaporized oil, withdrawingvaporous products from said fluid bed coking zone, and removing solidsfrom said coking zone for heating and passage to said delayed cokingzone and said fluid bed zone.

5. The process of claim 4 wherein about 70 to 90% of the totalconversion of said oil feed takes place in said delayed coking zone, andwherein said fluid bed zone operates at a temperature of about 950 to1050 F.

6. In a combination hydrocarbon oil lluid coking process wherein an oilis initially subjected to relatively 7 mild long timeconversionzconditions at a temperature in the range of 800 to 900 F. ina liquid ,phase delayed coking zone to produce vaporous euent,unvaporized oil and carbon deposits, and wherein the unconverted liquidresidue of said delayed coking zone is passed to the uid coking zone ofa two-vessel uid bed coking system comprising Va fluid coking zone `anda heating zone for conversion therein; the improvement which comprisespassing heated, relatively coarse solids averaging at least 100 micronsin diameter downwardly through said delayed coking zone to supply amajor portion of the requisite heat thereto along with serving as a sitefor deposition of carbon, maintaining said oil in said delayed cokingzone for a time suicient to obtain therein 70 to 90% of the totalultimate .conversion of said oil, passing said coarse solids along withunvaporized oil residue as a slurry from said delayed coking zone tosaid fluid bed coking zone, contacting said slurry'with a fluid bed ofReferences Cited in the file of this patent UNITED STATES PATENTS2,388,055 Hemminger Oct. 30, -1945 2,446,247 Scheineman Aug. 3, 19482,543,884 Weikart Mar. 6, 1951 2,605,214 Galstaun July 29, 19522,690,990 Adams et al. Oct. 5, 1954 2,719,114 Leffer Sept. 27, 1955

1. IN A COMBINATION HYDROCARBON OIL FLUID COKING PROCESS WHEREIN AN OIL IS INITIALLY SUBJECTED TO RELATIVELY MILD LONG TIME CONVERSION CONDITIONS AT A TEMPERATURE IN THE RANGE OF 800* TO 900*F. IN A LIQUID PHASE DELAYED COKING ZONE TO CAUSE SUBSTANTIAL CONVERSION TO VAPORS AND VAPORIZABLE LIQUID, AND THEN THE UNCONVERTED LIQUID RESIDUE OF SAID OIL AND SAID VAPORIZABLE LIQUID ARE PASSED TO THE FLUID COKING ZONE OF A TWO-VESSEL HYDROCARBON OIL FLUIDIZED SOLIDS COKING SYSTEM COMPRISING A FLUID COKING ZONE AND A HEATING ZONE TO BE FURTHER COMPLETELY CONVERTED TO COKE AND VAPORS; THE IMPROVEMENT WHICH COMPRISES PASSING PREHEATED SHOT OF RELATIVELY LARGE PARTICLE SIZE DOWNWARDLY THROUGH SAID LIQUID PHASE DELAYED COKING ZONE TO SUPPLY A MAJOR PORTION OF THE NECESSARY HEAT THERETO AND TO REMOVE COKE PRECURSORS THEREFROM, PASSING SAID SHOT ALONG WITH THE VAPORIZABLE LIQUID AND UNCONVERTED LIQUID RESIDUE TO SAID FLUID COKING ZONE WHEREBY SAID SHOT IS DRIED, THEN FLOWING SAID SHOT TO SAID HEATING ZONE ALONG WITH THE PORTION OF THE FLUIDIZED SOLIDS TRANSFERRED FROM SAID FLUID COKING ZONE TO SAID HEATING ZONE TO BE REHEATED THEREIN, AND SEPARATING AND RETURNING SAID SHOT SO REHEATED TO SAID DELAYED COKING ZONE. 